Programmable Data Planes COS 597 E Software Defined

Programmable Data Planes COS 597 E: Software Defined Networking Jennifer Rexford Princeton University MW 11: 00 am-12: 20 pm

Data Plane • Streaming algorithms that act on packets – Matching on some bits, taking a simple action – … at behest of control and management plane • Wide range of functionality – Forwarding and access control – Buffering, marking, shaping, and scheduling – Rewriting header fields (e. g. , NAT) – Traffic monitoring and deep packet inspection – Encryption, compression, and transcoding 2

A Need for Speed • High link speed – 10 Gbps, 40 Gbps, 100 Gbps • Small packets – 40 -byte TCP ACK packets • Small time per packet – 40 Gbps =124 Mpps with 320 -bit packets – 8 ns to process a packet • Routers need low latency – Relatively limited opportunity to batch or pipeline 3

A Range of Technologies • ASIC (App-Specific Integrated Circuit) – Fast, dense chip, but expensive to change • FPGAs and network processors – Fast, reconfigurable, hard to program • Graphics Processing Units – Massive parallel computation on small cores • Software on commodity computer – Easy to program, but I/O bandwidth, memory copying, and interrupt overheads 4

Click Modular Router

Click Motivation • Flexibility – Add new features and enable experimentation • Openness – Allow users/researchers to build and extend – (In contrast to most commercial routers) • Modularity – Simplify the composition of existing features – Simplify the addition of new features • Speed/efficiency – Operation (optionally) in the operating system – Without user needing to grapple with OS internals 6

Router as a Graph of Elements • Large number of small elements – Each performing a simple packet function – E. g. , IP look-up, TTL decrement, buffering • Connected together in a graph – Elements inputs/outputs snapped together – Beyond elements in series to a graph – E. g. , packet duplication or classification • Packet flow as main organizational primitive – Consistent with data-plane operations on a router – (Larger elements needed for, say, control planes)7

Push vs. Pull • Packet hand-off between elements – Directly inspired by properties of routers – Annotations on packets to carry temporary state • Push processing – Initiated by the source end – E. g. , when an unsolicited packet arrives (e. g. , from a device) • Pull processing – Initiated by the destination end – E. g. , to control timing of packet processing (e. g. , based on a timer or packet scheduler) 8

Click Language • Declarations – Create elements • Connections – Connect elements src : : From. Device(eth 0); ctr : : Counter; sink : : Discard; src -> ctr; ctr -> sink; • Compound elements – Combine multiple smaller elements, and treat as single, new element to use as a primitive class • Language extensions through element classes – Configuration strings for individual elements – Rather than syntactic extensions to the language 9

Handlers and Control Socket • Access points for user interaction – Appear like files in a file system – Can have both read and write handlers • Examples – Installing/removing forwarding-table entries – Reporting measurement statistics – Changing a maximum queue length • Control socket – Allows other programs to call read/write handlers – Command sent as single line of text to the server 10

An Observation… • Click is widely used – And the paper on Click is widely cited • Click elements are created by others – Enabling an ecosystem of innovation • Take-away lesson – Creating useful systems that others can use and extend has big impact in the research community – And brings tremendous professional value – Compensating amply for the time and energy 11